Traditionally, contact lenses were developed and marketed to be used on the external surface of the eye. Contact lenses were first manufactured using glass, although this was later substituted with biocompatible materials that minimize any reaction of the eye. Subsequently, the aphakic intraocular lens (“IOL”) was invented to replace the natural lens due to eye problems such as cataracts. Further development led to the posterior chamber phakic intraocular lens (“PCP-IOL”), which was particularly useful in younger patients having a functional natural lens.
Even after decades of development, however, PCP-IOLs suffer from a number of persistent drawbacks and shortcomings. In some instances, those drawbacks lead to serious complications for patients.
One drawback relates to the sizing of a PCP-IOL for a patient's specific anatomy. The challenge in sizing PCP-IOLs is that the ciliary sulcus, where the PCP-IOL is to be positioned, is significantly different from person to person. In fact, the size of the ciliary sulcus typically ranges between 10.5 mm and 13 mm. If a physician implants an undersized PCP-IOL for the patient's anatomy (FIGS. 20-21), the PCP-IOL may inadvertently contact the surface of the natural lens, thus affecting the precision of the lens system and possibly causing cataract formation. In addition, in cases involving PCP-IOLs for correcting astigmatism, an undersized lens can result in loss of corrective power of the PCP-IOL.
On the other hand, if a physician implants an oversized PCP-IOL for the patient's anatomy (FIG. 22-23), the PCP-IOL may result in complications as severe as glaucoma by pupillary blockage. In some cases, an oversized PCP-IOL leads to other complications. For example, implanting an oversized PCP-IOL can lead to pressure decompensation between the anterior and posterior chambers of the eye due to the pupillary blockage of the aqueous humor by the anterior part of the PCP-IOL, on the trabeculum. To avoid such blockage, physicians often perform an iridectomy in connection with a PCP-IOL implantation. An iridectomy is a surgical puncture of the iris that establishes a passageway for the proper flow of aqueous between the anterior chamber and the posterior chamber. However, to resolve the blockage problem without creating other complications, the iridectomy requires a highly skilled and experienced physician. Iridectomies are often times painful, or at least appreciably uncomfortable, for the patient.
As an alternative to an iridectomy, certain PCP-IOLs have been created with a central hole in the lens that allows flow of aqueous between the anterior and posterior chambers, considerably improving the pressure compensation or equalization between the chambers. But such a hole in the lens seriously degrades lens quality because it causes light scattering and dazzling. This, in turn, results in positive and/or negative dysphotopsia.
Yet another drawback with certain prior art PCP-IOLs is that they have an anterior surface or other parts that rasp or restrict movement of the iris during dilation of the pupil, thus causing depigmentation.